The invention pertains to a slurry pump with discharge cylinders, especially a two-cylinder concrete pump.
The principal method of operation of known slurry pumps, especially those utilized for the pumping of concrete, entails for two-cylinder piston pumps that both discharge pistons in the discharge cylinders, as a rule, are driven by hydraulic cylinders in such a way that while the one piston delivers, the other sucks in. The exchange of the piston play occurs always in the end positions of the stroke. The motion of the pistons are synchronized, i.e., when the hydraulic cylinder driving the discharge cylinder, e.g., is loaded on the piston side with hydraulic fluid (oil) , the oil displaced on the piston side is fed through a cross-over line to the piston rod side of the sucking discharge cylinder, so that the latter, due to identical surface ratios of the two drive cylinders, completes its intake stroke at the same speed as the advancing cylinder. Thereby, both pistons in the discharge cylinders always simultaneous reach their end positions.
Since each discharge cylinders in during the discharge stroke connected with the discharge line or respectively during the intake stroke with a charge funnel containing the slurry, a combinatorial circuit is required which reverses the concrete flow between the strokes after arrival at the end of the stroke, and which reverses the connection of the discharge cylinders with the discharge line or respectively with the charge funnel.
Typical for these and other slurry pumps is that between the discharge strokes, i.e. for the length of time of the change-over of the control organ, the delivery of the discharge cylinders comes to a halt. This causes an interruption of the slurry delivery. With the known slurry pump, the duration of the interruption is here further increased relative to the degree of filling, which depends on the air content, the flow resistance of the concrete, the suction speed as well as the cylinder diameter, i.e. by the length of time needed by the discharge cylinders at the beginning of the discharge stroke to compress the slurry.
To this comes a further unpleasant phenomenon, i.e. the back-flow of the slurry from the discharge line into the pumping cylinder during the switch-over phase of the concrete valve.
The interruptions of the delivery flow as a whole have a detrimental effect. The actual result is a pulsating delivery that causes vibrations. These have a particularly detrimental effect, if the slurry pump is installed on a vehicle and the discharge line is attached to a hinged distribution mast, since this results in an oscillatory system that shows resonance phenomena at the common cylinder stroke frequencies.
From this evolves the request to create a pump with which a continuous delivery stream can be obtained. In accordance with a state of the art (A) efforts have already been made to shorten the interruptions of the slurry delivery between the discharge strokes of the discharge cylinders or even to eliminate them.
In such an already known suggestion (U.S. Pat. No. 3 663 129), there from which the invention starts, is for this purpose a compensation cylinder, which that during the changeover of a swivel which is pipe constructed as a uniform hollow body, pushes slurry into the discharge line which during the subsequent discharge stroke of one of the two discharge cylinders is filled with slurry from the discharge line. This occurs with the outlet of the compensation cylinder, with the hollow body serving for the control of the concrete stream, being controlled in the same way as the openings of the discharge cylinders. The combinatorial circuit works with limit switches which are operated by the discharge cylinder pistons and initiates the intake or respectively the discharge stroke of the compensation cylinder.
A two-cylinder concrete pump of this type does not achieve the objective of a steady pumping of concrete through the discharge line. This is so , because such pumps lack the capability to compress the concrete that is drawn in each time and, therefore, cause at the beginning of each piston stroke a stoppage of the concrete flow.
According to another state of the art (B), i.e. of the DE-OS 29 09 964, it is known to achieve the concrete flow control with a pipe shunt (switch) that is realized by two S-shaped pipes. These pipes are arranged in the charge funnel in such a way that they can be swiveled and are bent like an "S". Each pipe is with its openings in continuous contact with a discharge line connection lying on a side of the charge funnel, while the other opening serves an entrance port and is alternatingly aligned with the opening of the discharge cylinder belonging to it, located on the opposite side of the charge funnel, or released so that the discharge cylinder opening is opened into the charge funnel and the cylinder is able to suck in the slurry.
The necessity to provide several swivel pipes for the control of the slurry flow results from the following. The discharge interruptions are not compensated for through the discharge stroke of a compensation cylinder. By that the combinatorial circuit controls the cylinder such that during the duration of the effective discharge stroke of a discharge cylinder, shortened by the degree of filling, the other discharge cylinder sucks in the slurry at substantially higher speed over a full stroke. In a first change-over step the swivel pipe valve belonging to this cylinder closes with its valve disk the opening of this discharge cylinder. The discharge cylinder subsequently to this also at increased speed executes a partial stroke corresponding to the missing fill volume and thereby compresses the drawn-in slurry. The assigned swivel pipe valve in a second change-over step reaches its end position, i.e. the discharge cylinder reaches with its precompressed slurry content a pump readiness position.
This last-mentioned state of the art is not only less favorable, because of the substantially higher speed for intake and compression stroke due to higher total switch-over time caused by multiple switch paths, but necessitates, due to the two required swivel pipe valves, a substantially higher technical expenditure.